Fixed: Used wrong groupId for getting ROI count

Fix for a problem @pwalczysko recently noticed: If images were moved to another group, the ROI count in the metadata panel was wrong.
Test: Add some ROIs to an image, make sure ROI count is correct (the value is not automatically updated, you'll have to refresh the metadata panel); move the image to another group and again make sure, that the ROI count is correct.

--no-rebase